A novel mass spectrometer with an external ionization source can be used to detect picogram quantities of compounds of biologic interest. The source contains a 63Ni foil, and is at atmospheric pressure. Samples are introduced in a flowing gas stream in selected common solvents. Positive ions are formed by a complex series of ion molecule reactions. The ionization reaction for the sample may involve either proton transfer or charge transfer. Negative ions are formed by either resonance or dissociative capture of thermal electrons, or by ion-molecule interactions. In a favorable case (very little adsorption on the reaction chamber walls), 5-10 picograms could be detected by single ion monitoring, and a scanned mass spectrum could be obtained with as little as 25 picograms. The potential uses include incorporation into LC-MS-COM and GC-MS-COM analytical systems.
Four alkaloids have been isolated from leaves of Ochrosia elliptica Labill. One has been shown to be identical with isoreserpiline. The other three, ellipticine, methoxyellipticine and elliptinine, have been characterized and certain features of their structures have been suggested.
The utility of combined gas chromatography-mass spectrometry in the analysis and characterization of sterols has been explored. Methylene unit (MU) values and principal mass spectrometric data are presented for trimethylsilyl ethers of 28 sterols, including the major natural sterols. The diagnostic value of the fragmentation of trimethylsilyl ethers of Delta(5)-3 beta-hydroxysteroids has been confirmed. Characteristic fragmentations of Delta(4)-3 beta-trimethylsilyloxysteroids, and of Delta(5,7)-3 beta-trimethylsilyloxysteroids were also found. Location of side-chain hydroxyl groups is facilitated by the alpha-cleavages typical of the trimethylsilyl ethers. Fragmentations of saturated sterols, and of Delta(7), Delta(8(9)) and Delta((14)) stenols, are less influenced by trimethylsilyl ether formation, but the derivatives still afford satisfactory mass spectra. The combination of gas chromatographic and mass spectrometric information allows positive identification of any of the sterols examined, whereas application of either technique alone may give inconclusive results.
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